Leigh,
JFBConnect doesn't have any built-in support for PayPlans. While we know of many sites that work with PayPlans, the flow you're looking for may not be possible with the current implementation.
With JFBConnect v6.0, we implemented a way for our socialprofile plugins to be able to control the registration process. We currently support that flow with Joomla, JomSocial and EasySocial. When configured, the user can authenticate from a social network but go through the alternate registration flow. The registration pages of those extensions can have data pre-filled by the social networks, but those extensions are completely in control of creating and activating the user.
Without a socialprofile plugin for PayPlans, right now, the only option is to let JFBConnect register the user and then redirect them to the PayPlans subscription page. Right now, as you noted, the user will be registered and activated by the time they visit the PayPlans page.
I hope that helps explain, and I'm sorry I don't have a better answer for you. If you contact PayPlans, feel free to refer them to this post. While we do plan to investigate tighter integration through a socialprofile plugin, if they want to work together on one, we may be able to get something out sooner.
Thanks,
Alex